Method of making dies



June 17,1958 I J; E. DALGLEISH ETAL 2,838,961

METHOD OF MAKING DIES Fild Jan. 20, 1954 2 Sheets-Sheet 1 INVENTORS FIG. 6 CARL '6. RICHTER ATTORNEY JOHN E. DALGLE/SH J ne 1 1958 'J. E. DALGLEISH ETAL 2,338,951

METHOD OF MAKING DIES Filed Jan. 20. 1954 I 2 Sheets-Sheet 2 INVENTORS JOHN E DALGLE/SH CARL 6f RICHTER BY WMJW ATTORNEY-S METHOD OF MAKING DIES John E. Dalgleish and Carl G. Richter, Cleveland, Ohio Application January 20, 1954, Serial No. 405,268

7 Claims. (Cl. 76107) (Granted under Title 35, U. S. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a method of forming a die for rocket motor combustion chambers and the like and to the chamber formed by the method.

Heretofore, in the formation of combustion chambers for various apparatus such as rocket motors, the usual procedure has been to form dies by the conventional diesinking methods. This involved use of expensive machinery, specialized equipment and the services of highly paid die-makers and die-sinkers; and, moreover, the casting made by these prior methods tended toward excessive Weight, and the loss of expensive metals in machining was large.

It is, therefore, an important object of this invention to provide a method of die formation which makes substantial reduction in construction cost, including manhours, metal materials, weight and skilled labor.

Another object is to provide a method of chamber die manufacture which is rapid in action and simple in manipulation.

Still another object is to provide a method of chamber formation which is based on a model, as a master pattern, without the shape or tolerances being reproduced from a blueprint.

An object also, is to permit use of original master patterns which may be hand-formed, machined, cast or molded from soft metal, plastic, wax, modeling clay and the like to eliminate initial cost.

A further and outstanding object of the invention is the fabrication of a rocket motor chamber of sheet metal to reduce weight and facilitate rapid and accurate construction.

Other objects and features of the invention, will become apparent on consideration of the following detailed description and accompanying drawing, inwhich:

Fig. 1 is a view in perspective of a mandrel shaped to conform to the desired die contour;

Fig. 2 is a view of the mandrel enclosed by the two concentric shells forming the rocket chamber;

Fig. 3 is a view illustrating the Wax strip Wound spirally around the shell unit of Fig. 2;

Fig. 4 is a cross section through a mold fashioned from the wax spiral of Fig. 3 and containing a plaster core;

Fig. 5 is a detail of the plaster core as coated by sprayed metal;

Fig. 6 is a view of one of the jacket half sections containing the metal shell die of Fig. 5;

Fig. 7 is a view of the shell unit of Fig. 2 placed in the other half die section;

States Patent 0 lice Fig. 8 is a view of the chamber shell unit expanded into thedie by hydraulic pressure; and

Fig. 9 is a view of a completed rocket combustion chamber.

In developing the method of the present invention use is made of a smoothsurfaced pattern or mandrel 10 (Fig. 1) of segmented parts, the parts 11 and 12 being separable at a screw joint 13, so as to permit placement and removal of the chamber wall sections. These wall sections are shown assembled on the mandrel, in Fig. 2, there being an outer wall 15 andan inner wall 16, the radial dimensions of the coaxial walls being such as to conform roughlyto the contour of the completed rocket chamber. The inner wall 16 is made of flat sheet metal cut from fiat stock with the aid of patterns fashioned on the mandrel shape. The steel sections are then formed to the approximate shape of the chamber by rolling up cones corresponding to the converging and diverging parts of the nozzle and a cylinder corresponding to cylindrical section of the chamber. These rolled sections are then welded together and the wall cold-formed on an engine lathe to the mandrel shape by use of a spinning roll.

The outer wall 15, which eventually forms the coolant jacket, is similarly made of sheet metal sections, which U are first formed and then welded together, both of these operations taking place over the first or inner wall, the

outer Wall, then, being cold spun tightly, with a metal-tometal fit .upon. the inner shell 16 and mandrel. The coldspinning is processed as for the inner shell 16, with the mandrel 10 inside the inner shell and with the mandrel ends operatively connected to a lathe, a spinning roll being used to force the outer Wall closely to the inner wall. The tapered cones, conforming to the mandrel shape, are then welded together at their small ends,

a cylindrical tube 17 secured to one of the enlarged ends,

and the terminals of inner and outer shells welded together. The wall sections of outer wall 15 are indicated by numerals 17.

Two small tubes, 18 and 19, are sealed to the outer shell to permit application of hydraulic pressure be tween the two walls, as will be more fully described hereinbelow:

The coolant passage die is made around the mandrel wall unit. To accomplish this result the desired final shape of the outer chamber wall is simulated by wrapping and attaching, as by glue, solid beeswax molding strips 20, of half-circular cross sections, to the outer wall 15, with the flat side of the molding facing inwardly, as shown in Fig. 3. Tapered wax strips are used where it is required to make a coolant passage of reduced secprovided as there arestrips attached. These strips are posite sides to form slots for reception of metal shims 25 (Fig. 4'), arid the alloy is then sprayed on the wax to form-'a temp'orary metal mold 26. the temperature of the alloy being insuflicient to melt the wax. The purpose of the shims 25 is to divide-the metal mold 26 into two symmetrical halves to facilitate manipulation in the plaster-of-Paris casting procedure. The shims are now removed, the wax cleaned from each half mold section, and the mold halves reassembled with the shims in place to form a tubular mold shell, the shell wall now being internally grooved in conformity to the wax strips. This shell form is now used to provide a receptacle for plaster of Paris 27 which is forced into the mold to form a model for the outer shell shape (Fig. 4). The mold metal "26 is now melted off the plaster 27 by placing the unit in boiling water or some such equivalent fluid heat, and the plaster cast thoroughly dried in a furnace for about twenty-four hours at atemperature of'250" F. To produce the final die formfor the outer chamber wall, the plaster cast is placed in a lathe and a shell 28 of steel is sprayed on the cast by any known high temperature metallizingprocess (Fig.

The plaster may now be removed and a suitable solid backing applied to the die shell. To accomplish these steps the die shell is centered in a thick walled metal cylinder made of two axially separated half sections 29, 30 each having apertured radial flanges for bolting the sections together, a retaining base plate 32, and top bolts 33 for retaining a cross top plate 34 during the pressurizing step. The flanges are spaced by shims 35 and are provided with aligning pins 36 with corresponding holes 37. Alloy metal is then poured into the cylinder cavity between the cylinder wall and the die shell, and, on solidification to form the backing 38, the shims 35 are removed and the die sawed lengthwise in the space between the cylinder flange left by shim removal to form the die sections 39, 40. New shims which on their inner edges conform to the die enclosure are prepared to take the place of the metal removed by the sawing step. Passages 41 for the pressurizing tubes 18 and 19 are cut in the die backing to form the final die form of Fig. 6.

To obtain a formed rocket chamber, the mandrel with the enclosing walls 15, 16 are placed between the die sections 39 and 40, Fig. 7 showing the rocket unit in the die section of backing plate 30. The die sections are then bolted together and hydraulic pressure of around 5000 pounds per square inch applied to the inlet 18. As a result the outer shell expands into the die convolutions thus producing the coolant passages 45. This pressurizing step averages about twenty seconds in time and the product has an accuracy of mold duplication within 0.003 inch. The pressurizing tubes 18, 19 are then removed from the unit and coolant connecting tubes 50, 51 are attached to the manifolds, as shown in the completed rocket unit 55 of Fig. 9. In addition, Fig. 9 shows the rocket combustion chamber 60 with annular nozzles 61 and channel spaces 62.

As an example of economy in use of the described method, in a typical operation there was a cost of only man-hours per unit as against 300 man-hours by previous methods. The saving of strategic rocket metal by weight was approximately 6 to 1 per unit. This is a saving of considerable magnitude in mass production, which is obviously applicable to this method.

It will now be apparent that the die may readily be made of sheet metal; that hydraulic pressure is adequate to secure exact conformation of the chamber wall with the die; that repeated die use is feasible with the sheet metal stock (over ten chambers can be made with one die without noticeable die wear); that the use of expensive and scarce materials is not required; and that scrap production is substantially reduced (the final chamber assembly contains about 60% of the starting metal).

The detailed procedures and materials hereinabove specified are by way of example for a clear understanding of the invention. Obviously, modification may be made. For example, for beeswax may be substituted plastic or modeling clay. For bismuth-tin may be subiii stituted kirksite, cerrosote, or other alloy with a melting point below the boiling point of water. For plaster of Paris may be substituted cement. For the steel of the final sprayed shell, bronze or any metal of adequate strength susceptible to spray deposition. It should also be apparent that the described die process may be applied to any intaglio design surfacing on sheet materials as well as to the specified grooves. Other modifications are possible and hence no specific limitations are implied except as may be required by the appended claims.

What is claimed is:

1. A method of forming a grooved plate which comprises attaching to one side of a pattern plate conforming in contour to the completed grooved plate plastic molding strips of the desired number and shape to simulate the surface of the completed plate, coating said strips with low melting point alloy material at a temperature insufiicient to melt said plastic strips to form a grooved metal mold, removing the mold from the plate and the plasticstrips from the mold, filling the mold grooves and contiguous joining spaces with a single mass of hardenable plaster, removing the mold from the plaster without disturbance of the plaster slurface, spraying the plaster with a hardenable substance to form a permanent grooved shell, removing the plaster, and backing the shell by deposition of a molten hardenable substance on the side of the shell opposite to the side of plaster application.

2. A method of making dies for the Walls of tubular devices having grooved surfaces, which comprises forming a smooth surfaced pattern tube having the overall dimensions of the desired device, attaching modeling plastic to the outer surface of said device in strip shape aligned to simulate the desired grooved surface, spraying the plastic strip with a form holding solid at a temperature insuflicient to melt the plastic to form a mold, removing the plastic from the mold, depositing a hardenable plaster on the grooved inner surface of said mold, removing the mold, depositing a layer of hardenable material on the outer surface of said plaster to form the die she'll, removing the plaster from said shell, and attaching a rigid backing to said shell outer surface.

3. A method of making dies for the walls of tubular devices having grooved surfaces, which comprises forming a smooth surfaced pattern tube having the overall dimensions of the desired device, attaching modeling plastic to the external surface of said tubular device in strip shape aligned to simulate the desired grooved surface, grooving the plastic on the tube at opposed sides along the tube length, inserting shims in said grooves, spraying the plastic with a form holding solid at a temperature insufircient to melt the plastic to form a mold, removing the shims and plastic from said mold to form mating mold sections, reassembling the mold sections free of said pattern tube with spacing shims between adjoining mold edges, depositing a hardenable fluent plaster inside said assembled mold filling the interior space thereof, removing the shims and mold, drying the plaster, forming a rigid coat on said plaster by spray deposition of hardenable substance to obtain the die shell, placing the die shell in a closed container with lengthwise shims on opposite sides thereof, placing a hardenable fluent material in said container adjoining said die shell to form a backing for the exterior of said die shell, removing said shims after said fluent material has hardened, severing said die shell and plaster in line with the grooves formed by said removed shims to form die sections, and removing the plaster from inside said die sections to form the die.

4. The method of making dies for the walls of tubular devices as defined in claim 3, with said modeling plastic-consisting of beeswax, said mold of bismuth-tin alloy, said plaster of plaster of Paris, and said die shell of steel.

5. A method of forming intaglio figures on sheet surfaces, which comprises attaching plastic masses, modeled to the desired form, to one side of a pattern sheet surface, coating said masses with low melting point alloy material at a temperature insufiicient to melt said plastic means to form a temporary metal mold, removing the mold from the sheet surface and the plastic masses from the mold, filling the mold depressions and joining spaces with a single mass of hardenable plaster, hardening said plaster, removing the temporary mold from the plaster without disturbance of the plaster surface, spraying the plaster with a hardenable substance to form a permanent mold of said plastic masses, removing the plaster, and attaching a rigid backing to the mold on the side opposite to the side of plaster application.

References Cited in the file of this patent UNITED STATES PATENTS Akin Apr. 9, 1929 Bateman July 12, 1932 Zinser July 26, 1932 Couse June 6, 1933 Ragsdale Nov. 21, 1933 Fitzgerald Mar. 13, 1934 Stossel Aug. 18, 1942 Grenell Sept. 28, 1954 Simmons Apr. 3, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2,838,961 June 17, 1958 John E. Dalgleish et al,

It is hereby certified that error appears in the printed specification of tfie' above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 23 for "slurface" read ms urfacej column 5, line 5 for "means" read .-mae;ses-r-=,

Signed and sealed this 7th day of October 1958.,

(SEAL) Attcst:

KARL H0 AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents 

